Internal combustion engines such as rotating machines (e.g. turbo machines such as gas turbines), or reciprocating machines (e.g. diesel engines), are subject to considerable loads. Creep and fatigue can affect the machines in extreme conditions owing to very high combustion temperatures, pressure ratios, and air flows. As a consequence of their deterioration, the main components of a gas turbine (GT), e.g., the inlet nozzle, the compressor, the combustion chamber, the turbine, the air flow cooler, and the outlet, can all contribute—to a different extent—to the degradation of GT performance. The condition of each single component invariably deteriorates with operation time, until it is at least partially restored by some maintenance action.
A goal of gas turbine performance diagnosis is to accurately detect, isolate and assess performance changes, system malfunctions and instrumentation problems. Among a number of other techniques, Gas Path Analysis (GPA), as disclosed for instance in EP-A 1 233 165, is a known framework for estimating shifts in performance from the knowledge of measured parameters, such as power, engine speeds, temperatures, pressures or fuel flow, taken along the gas path of the turbine. Discernable shifts in these measured parameters provide information for determining the underlying shift in engine operation from a presumed reference, nominal or initial state, i.e. the degradation symptoms. GPA allows engine performance deterioration to be identified in terms of a degradation of independent parameters or system states such as thermodynamic efficiencies, flow capacities and inlet/outlet filter areas. In a subsequent diagnosis step, these degradation symptoms are analysed and a maintenance action schedule is deduced, for ensuring economic and safe operation, or a prediction of the remaining life of the major components is made. The origin of a fault affecting a given component of the gas turbine can be of various natures, such as a contamination of compressor blades, erosion of turbine blades or corrosion of machine parts, for example. Conversely, different faults often create similar observable effects or degradation symptoms.
Accordingly, for the operation of a GT, it can be important to know exactly the main process states such as temperatures, pressures or fluid mass flow, before and after each component. Specifically, the turbine inlet temperature is constrained to an upper limit, as high temperatures let the turbine blades deteriorate faster than lower temperatures, thereby reducing the life time of the GT. On the other hand, for fuel efficient operation of a GT, high temperatures are desired. Therefore, the turbine inlet temperature is controlled tightly. However, in many GT's the turbine inlet temperature is not measured but derived from other measurable states, which can produce uncertainty on the controlled variable. Reliable methods to derive turbine inlet temperatures are therefore desired for operating a GT efficiently. Precise knowledge of these unmeasured states makes it possible to better estimate the operating conditions and, therefore, to better predict maintenance scheduling.
Known methods of determining unknown process states use a dynamic or static model. These models are based on thermodynamic and fluid mechanical principles. Model-based techniques make use of Kalman filter techniques for the online estimation of the unknown states or use iterative methods (e.g. Newton-Raphson), such as described in EP 1 233 165. However, these methods can be impacted negatively in that the fluid flowing through the GT can influence considerably the unmeasured states, e.g. ambient humidity (in form of vapour) cools the turbine inlet temperature owing to the vaporization energy. Often this effect is compensated by applying empirical correction curves. This effect is also used to lower the temperature in the combustion chamber in order to reduce NOX emission when the GT is operated with liquid fuel (oil) instead of gaseous fuel. Generally, the combustion is not modelled and, therefore, the composition of air (influenced by the ambient humidity) and of the exhaust gas (influenced by fuel and air composition) and the corresponding mass flows are not considered.
The disclosures set forth in the documents mentioned herein are incorporated by reference in their entireties.